Many articles of manufacture have structural components, the exterior surfaces of which define a compound surface, for example, automobile door panels, fenders, hoods, and the like. The exterior surfaces of these compound structural components have been painted by various techniques in order to apply a protective and decorative coating thereto. There have been improvements made in the paints and in the application equipment, yet the basic features of the commercially used processes remain essentially unchanged. In general, a paint is reduced to a satisfactory viscosity with solvent(s), and is then applied or propelled onto the surface of the end product. Solvent is then allowed to evaporate into the air at point of application and also in bake ovens used to cure or dry the paint. The pollution resulting from the evaporation of the volatile compounds used as paint solvents has led to the use of expensive solvent collectors and afterburners to reduce this pollution.
The paint industry has developed coatings that have reduced solvent content, but they still do not meet many environmental, performance, or economic requirements. Electrostatic application devices have been designed to develop high transfer efficiencies, however, the solvent has to be discharged in ovens, if not in a spray booth.
Heat-vacuum application of decals, woodgrain prints, signing, etc. has been common practice in the art. The conventional practice involves the contact placing of a film article, coated with a heat-activatable adhesive, onto an application surface or workpiece.
Among the problems experienced by the industry or cited in the art, are:
(1) composites that can't be applied to three dimensional contours without the bubbles and wrinkles caused by pre-adhesion; PA1 (2) solvent emissions at component assembly sites; PA1 (3) finished coatings that are not sufficiently durable and impact-resistant; and PA1 (4) adhesives having poor adhesive performance under varying environmental conditions.
U.S. Pat. No. 4,263,077 (Rampelberg) discloses "an in-press method for applying a painted surface to a piece of hardboard or fiberboard while the board is being formed in a press", wherein a hardened paint coat comprising abrasion-resistant clear coat, paint layers, and an adherence coat, [phenolic type], on a carrier is placed in a press with exploded fibers (e.g., wood) and compressed under heat and pressure to form a rigid and dense hardboard piece and transfer the hardened paint coat from the carrier to the board. The clear coat and paint layers are sufficiently heat-resistant that "they remain hardened when subjected to board-forming temperatures at least above 400.degree. F." (column 3, lines 57-59 and column 4, lines 27-28) such that they will not thermoplastically deform at temperatures at which the board is formed. Accordingly such paint coats can not be conformed to surfaces such as automotive body parts having nonplanar contours.
U.S. Pat. No. 3,907,974 (Smith) discloses a heat transfer decoration comprising, in sequence, a carrier, a transfer lacquer layer removably adhered thereto, at least one design print layer adhered to the lacquer layer, and a heat-activatable adhesive layer adhered over the design print layer wherein at least one of the transfer lacquer or design print layer contains a cross-linkable resin and a cross-linking agent for cross-linking the resin intralayer, and preferably interlayer, to form a unified adherent decoration resistant to abrasion and chemicals which is preferably thermoset throughout its thickness. Such a decoration would not be expected to provide desired impact resistance, especially at low temperatures.
U.S. Pat. No. 3,928,710 (Arnold et al.) discloses a heat transfer material comprising a polyethylene terephthalate film carrier, an essentially unpigmented thermoplastic layer of hard acrylic resin, and a thermoplastic image layer for transfer to articles such as soft vinyls to which the image layer will adhere. Upon being contacted to a substrate and application of heat, the image layer softens to bond to the surface of the substrate and the clear acrylic layer releases from the carrier, whereupon the carrier may be removed to effect transfer. The reference does not teach that such articles will provide desired impact resistance.
U.S. Pat. No. 4,451,522 (de Vroom) discloses a transferable enamel sheet comprising a carrier film, a release layer, a paint or enamel layer, and a pressure-sensitive type adhesive layer. The formulation of adhesive disclosed therein would not be expected to provide the desired combination of glass transition temperature and tensile modulus necessary to provide desired impact-resistance and broad temperature stability.
U.S. Pat. No. 3,640,791 (Rosenheim) discloses a paint transfer process for automobiles and a transfer article comprising, in sequence, a release liner, a layer of paint releasably adhered thereto and a layer of water-activatable or pressure-sensitive adhesive. This article is generally described in the reference as a patch. The articles disclosed in Rosenheim would typically be difficult to apply to large or contoured surfaces because of the tacky nature of the adhesive would tend to result in undesired preadhesion. Furthermore, the articles disclosed in the reference are not taught to be impact-resistant.
U.S. Pat. No. 4,101,698 (Dunning et al.), discloses a film laminate construction comprising an elastomeric film, such as polyurethane, a reflective layer, and a layer of heat-activatable or pressure-sensitive adhesive on a temporary release carrier, the elastomeric film being in contact with the release carrier. Such laminates are taught to be elastomeric and accordingly are not well-suited for applications where they are stretched when conformed to a surface, e.g., an indented surface, because they would tend to return to their original dimensions and shape, thus tending to shrink, separate, or "pop-off" from the surface.
In International Publication No. WO84/03473 (Boyd), the title of which is "Heat Transfer Pad Decoration and Substrate Therefor", a heat transfer product for a contoured surface is described. The product consists of a polyamide adhesive/release coating on a paper liner, printed with an ink and protected with a clear coat. The polyamide is referred to as an adhesive/release coating because it releases from the paper when heated and acts as a hot melt adhesive when in contact with a substrate. The transfer is picked up with a hot silicone sponge from the paper and pressed onto the contoured application surface. The polyamide creates a bond and the sponge then releases. The articles disclosed in the reference would not be expected to provide desired broad temperature performance.
In summary, a need exists in the art for a paint composite that can be applied easily and inexpensively and yet will provide a durable protective coating over a range of thermal environments.